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HIERARCHICAL CLASSIFICATION OF THE CLASS STEGOCEPHALI+

HIERARCHICAL CLASSIFICATION OF THE CLASS STEGOCEPHALI+

EUKARYA>UNIKONTA>OPISTHOKONTA>ANIMALIA>BILATERIA>DEUTEROSTOMATA>VERTEBRATA>TETRAPODA>STEGOCEPHALI
CLASS STEGOCEPHALI LINKS

Description of Class

The following descriptions come from Benton (2005) and Nelson (2006). The structure of the following system is also based, in part, on the phylogenetic treatment by Mikko’s Phylogeny Web (from the Finnish Museum of Natural History). Taxa in red are extinct.
  • CLASS STEGOCEPHALI[i] +
  • A class with a single order and 8 paraphyletic families.
    • ORDER UNNAMED
      • FAMILY ELGINERPETONTIDAE
      • Upper Devonian
      • Elginopteron
      • FAMILY ICHTHYOSTEGIDAE
      • Freshwater. Fishlike in form with functional gills as adults. Therefore, primarily aquatic. Particularly massive ribs. Broad tail with a swimming fin and lateral line system. The bones of the ankles and wrists were weak. Skull very much like that of Euthenopteron, Panderichthyes, and Tiktaalik (sarcopterygians). Seven toes front and back; and the foot was paddle-like.
      • Upper Devonian
      • Ichthyostega
      • FAMILY ACANTHOSTEGIDAE
      • Freshwater. The animal was very similar to Ichthyostega except that it had a shorter skull and shorter gill coverings. Also, its ribs were quite small. Eight toes front and back, foot paddle-like. Clearly adapted primarily for an aquatic lifestyle.
      • Upper Devonian
      • Acanthostega
      • FAMILY TULERPETONTIDAE
      • Similar to Acanthostega and Ichthyostega but found in marine sediments.
      • Upper Devonian
      • Tuleropteron
      • FAMILY COLOSTEIDAE
      • Aquatic with lateral line system. Very long body with 40 trunk-neck vertebrae. Broad tail. Eyes placed forward. Along with the smaller teeth, they had some large, fang-like teeth.
      • Lower Carboniferous (Mississippian)
      • Greererpeton
      • FAMILY CRASSIGYRINIDAE
      • Members of this family remained aquatic as evidenced by a diminutive forelimb and reduced hind limb. It had a long body and likely had a large flattened tail. The mouth had large teeth and the skull retained a notch that is interpreted as a spiracle opening.
      • Lower Carboniferous (Mississippian)
      • Crassigyrinus
      • FAMILY WHATCHEERIIDAE
      • They had a leg and foot adapted to walking rather than swimming. The feet were pentadactyl.. In their compliment of teeth, they had at least one pair of massive teeth on the upper jaw. They retained the fish-like teeth on the upper palate. They had a somewhat high rather than flattened skull.
      • Lower Carboniferous
      • Whatcheeria, Pederpes
      • FAMILY BAPHETIDAE
      • Also called the loxommatids, these had very low skulls (the lower jaw was thicker than the cranium-upper jaw complex) with an unusual opening in front of the orbit (for a gland?). They had sharp pointed teeth with 6 or more fangs attached to the palate. They had traces of a lateral line. They seem to have developed a muscle for opening the mouth that ran from the back of the articulation of the joint to the side of the skull, a structure unlike fish and much like later tetrapods. Aspects of the postcranial skeleton are not known.
      • Lower Carboniferous (Mississippian)
      • Megalocephalus, Baphetes, Loxomma, Spathicephalus.
[i] I use this term in the old, more narrow sense to include all of the basal tetrapod families. In a strict phylogenetic interpretation, Stegocephali would include all of the gnathostome animals with digits.
LITERATURE CITED

Ahlberg, P.E., J.A. Clack, and H. Blom. 2005. The axial skeleton of the Devonian tetrapod Ichthyostega. Nature 437(1): 137-140.

Ahlberg, P.E., J.A. Clack, E. Luksevics, H. Blom, and I. Zupins. 2008. Ventastega curonica and the origin of tetrapod morphology. Nature. 453: 1199-1204.

Benton, M. J. 2005. Vertebrate Paleontology. Third Edition. Blackwell Publishing, Malden, MA.

Callier, V., J.A. Clack, and P.E. Ahlberg. 2009. Developmental trajectories in the earliest known tetrapod forelimbs. Science. 324: 364-367.

Clack, J.A. 1994. Acanthostega gunnari, a Devonian tetrapod from Greenland; the snout, palate and ventral parts of the braincase, with a discussion of their significance. Meddelelser om Grønland: Geoscience. 31: 1-24.

Clack, J.A. 1997. Devonian tetrapod trackways and trackmakers: a review of the fossils and footprints. Paleogeography, Paleoclimatology, Paleoecology. 130: 227-250.

Clack, J. A. 2002. An early tetrapod from ‘Romer’s Gap’. Nature 418: 72–76.

Clack, J.A. 2009. The fish-tetrapod transition: new fossils and interpretations. Evo Edu Outreach. 2: 213-223.

Coates, M.I. and J.A. Clack. 1990. Polydactly in the earliest known tetrapod limbs. Nature 347: 66-69.

Jarvik, E. 1952. On the fish-like tail in the ichthyostegid stegocephalians. Meddelelser øm Grönland. 114(2): 1-90.

Coates, M.I. and J.A. Clack. 1991. Fish-like gills and breathing in the earliest known tetrapod. Nature. 352: 234-236.

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Daeschler, E.B. and N. Shubin. 1995. Tetrapod Origins. Paleobiology. 21(4): 404-409.

Daeschler, E.B., N.H. Shubin, K.S. Thomson and W.W. Amaral. 1994. A Devonian tetrapod from North America. Science. 265: 639-642.

Hinchliffe, R.J. 2002. Developmental basis of limb evolution. Int. J. Biol. 46: 835-845.
Janvier, P. 1996. Early Vertebrates. Claredon Press. Oxford.

Laurin, M. 2002. Tetrapod phylogeny, amphibian origins, and the definition of the name Tetrapoda. Syst. Biol. 51: 364-369.

Lebedev, O.A. 1984. “The first find of a Devonian tetrapod in USSR.” Doklady Akad. Navk. SSSR. 278: 1407-1413. (in Russian)

Lebedev, O.A. and J.A. Clack. 1993. “Upper Devonian tetrapods from Andreyeva, Tula Region, Russia.” Paleontology 36(3): 721-734.

Lebedev, O.A. and M.I. Coates. 1995. “The postcranial skeleton of the Devonian tetrapod Tulerpeton curtum Lebedev”. Zoological Journal of the Linnean Society 114: 307-348.

Nelson, J. S. 2006. Fishes of the World. 4th edition. John Wiley and Sons, Inc. New York.

Ruta, M., M. I. Coates, and D. L. J. Quicke. 2003. Early tetrapod relationships revisited. Biol. Rev. 78:251-345.

Ruta, M., J. E. Jeffery, and M. I. Coates. 2003. A supertree of early tetrapods. Proc. R. Soc. Lond. B. 270: 2507-2516.

Shubin, N.H. and P. Alberch. 1986. A morphological approach to the origin and basic organization of the tetrapod limb. In: Hecht, M.K., B. Wallace, and G. Prance. Evolutionary Biology. Plenum Press. New York pp. 319-387.

Shubin, N.H., E.B. Daeschler, and F.A. Jenkins. 2006. The pectoral fin of Tiktaalik roseae and the origin of the tetrapod limb. Nature. 440: 764-771.
By Jack R. Holt. Last revised: 01/19/2013
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